Internal combustion engine ignition devices having an ignition plug and an ignition coil that are integrated with each other are proposed in various kinds. For quality inspection of the ignition coil, a voltage generated in the ignition coil is measured. An electrical discharge from the ignition plug must be prevented during the voltage measurement. However, the ignition plug in complete products cannot be prevented from the electrical discharge. As a result, the quality inspection of the ignition coils cannot be properly performed.